The other day I passed a subway poster for Adam Sandler’s new comedy Jack and Jill with ”NOT FUNNY” scrawled across Sandler’s forehead. If the citizen-critic was referring to the saturation-carpet-bomb movie trailer that has been scarring our eyeballs for the past few weeks, then, like, right on: That thing is painful.

But if the comment was just generally lobbed in the direction of Sandler’s head, then a clarification is in order. Adam Sandler is obviously funny to his audience, his base, his peeps who know what to expect from an Adam Sandler comedy. Am I right? Anybody? Some of his movies are mushy and others more sour. Some are more blithely gross, others tilted more towards anger. Often they’re built around a core of male childishness and usually they end up cuddled in a soft heap of family values. But in one form or another, you get exactly what you pay for at an Adam Sandler comedy. Otherwise the man wouldn’t have earned zillions.

Anyhow, Jack and Jill is not not funny. It’s just unreliably, haphazardly funny when it’s not just obnoxiously sentimental or plain obnoxious. And for anyone less than a Sandler loyalist — for someone like me — that sloppy hodgepodge approach is exhausting. Maybe you’re different? The joke is that Sandler plays fortysomething Jack Sadelstein, a successful Los Angeles ad executive, husband, and father of two, and he also plays Jill Sadelstein, Jack’s braying, neurotic, unmarried fraternal-twin sister from hometown Bronx, N.Y. Jack is proudly Jewish: The family celebrates Hanukkah (as well they should, since Sandler pretty much put that minor winter holiday on the map with his Hanukkah song). But most of Jack’s jagged Jewish edges have been well smoothed by economic success and geographical distance from his Bronx childhood. His wife (poor, bereft Katie Holmes, given absolutely nothing of consequence or interest to do) is a classy-looking convert to Judaism, and their young son is adopted from India. (Their little biological daughter dresses in a Pilgrim costume for Thanksgiving.) Jill, on the other hand, with her yawping New York borough accent, her abrasive coarseness of manner, her overdone, inappropriate wardrobe and makeup, and her shtetl mentality (”What’s the Internet?” she screeches), is the uncouth, unrenovated Jewish sibling. She says the wrong thing, she’s needy, she’s insensitive to social cues, she’s zaftig and uncoordinated and self-pitying and sweaty and quick to take offense.

Jill drives Jack crazy with antics that take up most of the movie, until Jack realizes in the end that his sister is really a good-hearted horror, and that he, Jack, loves Jill, and that it’s worth putting up with her thin-skinned craziness once a year because that’s what family is about. (Once a year at holiday time, at least, because that’s what counts as family time these days.) Yeah yeah yeah, happy Festivus and all that. But meanwhile, in another corner of the movie, Sandler and his frequent, slaphappy director Dennis Dugan sign off on fascinating craziness of an entirely different kind, this time from no less a big-deal thespian than Al Pacino. The grand star plays ”Al Pacino” — to be sure, a cockeyed version — and when we first meet him, this Al is on stage in a production of Shakespeare’s Richard III, mad as hell because the ringing of some idiot’s mobile phone in the audience has distracted him. Pacino is not generally a ”funny” actor, but playing this version of himself — an eccentric star who develops an obsessive crush on Jill because he responds to her realness, her rawness, her glass-shattering Bronx inflections — he’s a weird figure of nutty fun. You don’t know Al until you’ve seen him wooing an Adam Sandler who’s dolled up in shticky drag. But you do know Sandler. So make your ticket selection accordingly. D+